This invention relates in general to drive train systems for transferring rotational power from a source of rotational power to a rotatably driven mechanism. In particular, this invention relates to an improved driveshaft assembly for use in such a drive train system that is axially collapsible in the event of a collision to absorb energy.
Torque transmitting shafts are widely used for transferring rotational power from a source of rotational power to a rotatably driven mechanism. For example, in most land vehicles in use today, a drive train system is provided for transmitting rotational power from an output shaft of an engine/transmission assembly to an input shaft of an axle assembly so as to rotatably drive the wheels of the vehicle. To accomplish this, a typical vehicular drive train system includes a hollow cylindrical driveshaft tube. A first universal joint is connected between the output shaft of the engine/transmission assembly and a first end of the driveshaft tube, while a second universal joint is connected between a second end of the driveshaft tube and the input shaft of the axle assembly. The universal joints provide a rotational driving connection from the output shaft of the engine/transmission assembly through the driveshaft tube to the input shaft of the axle assembly, while accommodating a limited amount of misalignment between the rotational axes of these three shafts.
A recent trend in the development of passenger, sport utility, pickup truck, and other vehicles has been to design the various components of the vehicle in such a manner as to absorb energy during a collision, thereby providing additional safety to the occupants of the vehicle. As a part of this trend, it is known to design the drive train systems of vehicles so as to be axially collapsible so as to absorb energy during a collision. To accomplish this, the driveshaft tube may be formed as an assembly of first and second driveshaft sections that are connected together for concurrent rotational movement during normal operation, yet which are capable of moving axially relative to one another when a relatively large axially compressive force is applied thereto, such as can occur during a collision. A variety of such axially collapsible driveshaft assemblies are known in the art.
It has been found to be desirable to design axially collapsible driveshaft assemblies of this general type such that a predetermined amount of force is required to initiate the relative axial movement between the two driveshaft sections. It has further been found to be desirable to design these axially collapsible driveshaft assemblies such that a predetermined amount of force (constant in some instances, varying in others) is required to maintain the relative axial movement between the two driveshaft sections. However, it has been found that the manufacture of such axially collapsible driveshaft assemblies is somewhat difficult and expensive to manufacture than convention non-collapsible driveshafts. Thus, it would be desirable to provide an improved driveshaft assembly for use in a vehicular drive train system that is axially collapsible in the event of a collision to absorb energy and that is relatively simple and inexpensive in structure.
This invention relates to an improved driveshaft assembly for use in a vehicular drive train system that is axially collapsible in the event of a collision to absorb energy and that is relatively simple and inexpensive in structure. The driveshaft assembly includes a driveshaft that is preferably formed from a single piece of material having a constant diameter. However, a controlled collapse zone is formed in the interior of the driveshaft. The controlled collapse zone includes a collapse initiation portion, a collapse distance control portion, and a collapse termination portion. The collapse initiation portion extends from a first normally sized portion of the driveshaft and is preferably formed having a generally semi-circular bulge or bump shape that extends a relatively short axial distance. Preferably, the collapse initiation portion is formed having a diameter that is somewhat larger that the normal diameter of the driveshaft. The collapse distance control portion extends from the collapse initiation portion and is preferably formed having an elongated cylindrical shape that extends a relatively long axial length. Preferably, the collapse distance control portion is formed having a diameter that is slightly larger than the normal diameter of the driveshaft, but smaller than the diameter of the collapse initiation portion. The collapse termination portion extends from the collapse distance control portion to a second normally sized portion of the driveshaft and is preferably formed having a frusto-conical shape that extends a relatively short axial length. Preferably, the collapse termination portion tapers at a constant angle from the diameter of the collapse distance control portion to the normal diameter of the driveshaft.